Semiconductor processing method of forming a conductively doped semiconductive material plug within a contact opening

ABSTRACT

A semiconductor processing method of forming a conductively doped semiconductive material plug within a contact opening includes, a) providing a node location and a plug molding layer outwardly thereof; b) providing a contact opening through the plug molding layer to the node location; c) providing a first layer of semiconductive material over the molding layer to within the contact opening, the first layer thickness being less than one-half the contact opening width to leave a first remaining opening, the first layer having an average conductivity enhancing dopant concentration from 0 atoms/cm 3  to about 5×10 18  atoms/cm 3  ; d) after providing the first layer, increasing the average conductivity enhancing dopant concentration of the first layer to greater than or equal to about 1×10 19  atoms/cm 3  ; e) after increasing the dopant concentration of the first layer, providing a second layer of semiconductive material over the first layer and to within the first remaining opening, the second layer having an average conductivity enhancing dopant concentration from 0 atoms/cm 3  to about 5×10 18  atoms/cm 3  ; f) after providing the second layer within the first remaining opening, increasing the average conductivity enhancing dopant concentration of the second layer to greater than or equal to about 1×10 19  atoms/cm 3  ; and g) providing the contact opening to be substantially filled with semiconductive material having an average conductivity enhancing dopant concentration of greater than or equal to about 1×10 19  atoms/cm 3  to define a conductively doped semiconductive material plug within the contact opening.

RELATED PATENT DATA

This patent resulted from a file wrapper continuation application ofU.S. patent application Ser. No. 08/580,631, now abandoned.

TECHNICAL FIELD

This invention relates to semiconductor processing methods of formingconductively doped semiconductive material plugs within contactopenings.

BACKGROUND OF THE INVENTION

In the processing of integrated circuits, electric contact must be madeto isolated active device regions formed within a wafer/substrate. Theactive device regions are connected by high electrically conductivepaths or lines which are fabricated above an electrically insulativematerial, which covers the substrate surface. To provide electricalconnection between the conductive path and active-device regions, anopening in the insulator is provided to enable the conductive films tocontact the desired regions. Such openings are typically referred to ascontact openings, or simply as "contacts". The term also applies to anyopening provided in an insulating layer to make electrical connection toa lower elevation conductive node. The contacts are typically filledwith a highly conductive material, with the resultant constructionconstituting a plug within the contact opening.

Further, multi-level metalization is a critical area of concern inadvanced semiconductor fabrication where designers continue to strivefor circuit density maximization. Metalization interconnect techniquestypically require electrical connect between metal layers or runnersoccurring at different elevations within a semiconductor substrate. Suchis typically conducted, in part, by etching a contact opening throughinsulating material to the lower elevation metal layer. Increasedcircuit density has resulted in narrower and deeper electrical contactopenings between layers within the substrate. Adequate contact coveragewithin these deep and narrow contacts continues to challenge thedesigner.

The electrically conductive filling material utilized for fillingcontact openings typically comprises conductively doped polysilicon ormetal. In the context of this document, "metal" is intended to broadlydefine any metal alloy, elemental metal, or metal compound whoseelectrically conductive properties are defined by a resistivity lessthan 2000 microohm-cm. Further, combinations of these materials areoften used. For example, metal or metal compounds are typically utilizedwithin contact openings to provide suitable interconnection and barrierlayers between underlying substrates and overlying conductive materials.

As contact openings become narrower and deeper, it becomes moredifficult for the artisan to completely fill the contact openings. Onepreferred method of depositing polysilicon in a manner having highconformality is by chemical vapor deposition. In such processes,reactive gases are combined within a chemical-vapor deposition reactorunder conditions effective to deposit a desired film, such as silicon,atop the wafer and conformally within deep contact openings. One typicalprocess for depositing polycrystalline silicon includes feeding ofsilane gas to a reactor with the substrate maintained at a temperatureof 650° C., with the reactor ambient being at 80 Torr. Such will providea highly conformal layer of polycrystalline silicon as-deposited to deepwithin narrow contact openings. However, such polysilicon as-depositedwill effectively function as an electrically insulative material.Polysilicon can be rendered electrically conductive by providingconductivity enhancing impurity dopants into the layer either during orafter deposition. One after-deposition technique is by ion implantation.However, this technique is largely ineffective for doping materialwithin a long, deep contact opening.

Doping can be provided in situ by combining dopant impurity gases withthe silane or other silicon precursor gas during the deposition process.The typical average concentration of dopant impurity required to produceadequate electrical conductivity exceeds 1×10²⁰ atoms/cm³. Howeverunfortunately, conformality in the deposition diminishes significantlyin in situ processes which provide dopant impurity concentration ofhigher than 5×10¹⁸ atoms/cm³.

The problem is illustrated in FIG. 1. There, a semiconductor waferfragment 10 includes a bulk silicon substrate 12, a field effecttransistor gate construction 14 and adjacent source/drain diffusionregions 16 and 18. An insulating layer 20, or other suitable contactopening molding layer, is provided outwardly of substrate 12 over gate14 and diffusion regions 16 and 18. A contact opening 22 is cuttherethrough for outwardly exposing and making electrical connectionwith diffusion region 18. A layer 24 of polysilicon having conductivityenhancing impurity dopant of greater than or equal to about 5×10¹⁸atoms/cm³ is deposited atop molding layer 20 to within contact opening22. However due to the high dopant concentration, contact opening 22 isless than completely filled, leaving an undesired void or key-hole 25therewithin.

It would be desirable to develop alternate processes which enableprovision of heavily doped polysilicon or other semiconductive materialplugs within contact openings having a conductivity dopant impurityconcentration of greater than 5×10¹⁸ atoms/cm³ which are free of suchvoids.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a prior art semiconductorwafer fragment and is discussed in the "Background" section above.

FIG. 2 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with the invention.

FIG. 3 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 4.

FIG. 6 is a diagrammatic sectional view of an alternate embodimentsemiconductor wafer fragment at a processing step in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of the invention, a semiconductorprocessing method of forming a conductively doped semiconductivematerial plug within a contact opening comprises the following steps:

providing a node location to which electrical connection with aconductively doped semiconductive material plug is to be made;

providing a plug molding layer outwardly of the node location;

providing a contact opening through the plug molding layer to the nodelocation, the contact opening having an opening width;

providing a first layer of semiconductive material over the moldinglayer to within the contact opening, the first layer being provided to athickness which is less than one-half the contact opening width to lessthan completely fill the contact opening with the first layer and leavea first remaining opening, the first layer of semiconductive materialhaving an average conductivity enhancing dopant concentration from 0atoms/cm³ to about 5×10¹⁸ atoms/cm³ ;

after providing the first layer within the contact opening, increasingthe average conductivity enhancing dopant concentration of the firstlayer to greater than or equal to about 1×10¹⁹ atoms/cm³ ;

after increasing the dopant concentration of the first layer, providinga second layer of semiconductive material over the first layer and towithin the first remaining opening, the second layer of semiconductivematerial having an average conductivity enhancing dopant concentrationfrom 0 atoms/cm³ to about 5×10¹⁸ atoms/cm³ ;

after providing the second layer within the first remaining opening,increasing the average conductivity enhancing dopant concentration ofthe second layer to greater than or equal to about 1×10¹⁹ atoms/cm³ ;and

providing the contact opening to be substantially filled withsemiconductive material having an average conductivity enhancing dopantconcentration of greater than or equal to about 1×10¹⁹ atoms/cm³ todefine a conductively doped semiconductive material plug within thecontact opening.

Referring to FIG. 2, a semiconductor wafer fragment in process isindicated generally with reference numeral 26. Such comprises a bulksilicon substrate 27, a word line or gate construction 28, and adjacentsource/drain diffusion regions 29 and 30. In the context of thisexample, the upper surface of substrate 27 at diffusion region 30constitutes a node location to which electrical connection with aconductively doped semiconductive material plug is to be made. A plugmolding layer 32 is provided outwardly of substrate 27, word line 28 anddiffusion regions 29 and 30. Such preferably predominantly comprisesSiO₂, such as borophosphosilicate glass (BPSG). A contact opening 34 isprovided through molding layer 32 to node location 30. For purposes ofthe continuing discussion, contact opening 34 has an opening width "A".By way of example only, an example "A" width is 4000 Angstroms, with anexample depth of contact opening 34 being 20,000 Angstroms. A firstlayer 36 of semiconductive material is provided over molding layer 32 towithin contact opening 34 to a thickness which is less than one-halfcontact opening width "A". Thus, contact opening 34 is less thancompletely filled with first layer material, leaving a first remainingopening 38. As deposited, first layer 36 of semiconductive material isprovided to have an average low conductivity enhancing dopantconcentration from 0 atoms/cm³ to about 5×10¹⁸ atoms/cm³. Such willfacilitate provision of a highly conformal layer within contact opening34 as shown.

Referring to FIG. 3, the average conductivity enhancing dopantconcentration of first layer 36 is increased to a value greater than orequal to about 1×10¹⁹ atoms/cm³, and preferably to a value at least asgreat as 5×10²⁰ atoms/cm³ to provide effective resultant electricalconductivity thereof, and modified layer 36a. Example techniques forincreasing or inherently providing such higher concentration of impuritydopants would include ion implantation (less preferred) or gas diffusion(most preferred). Example dopant gases include PH₃, AsH₃ and B₂ H₆.Preferably, gas diffusion is conducted in the same chemical vapordeposition reactor in which layer 36 was provided. For example oncelayer 36 is provided to its desired thickness, the flow of precursorgases fed to the reactor could be ceased and provision of a conductivityimpurity dopant gas, such as phosphine, added or be significantlyincreased to the reactor and maintained therein for a period of timesuitable to provide the desired resultant impurity concentration ofgreater than 1×10¹⁹ atoms/cm³. Alternately but less preferred, the gasdiffusion or other doping could be conducted in a separate reactor orcontrolled chamber.

Referring to FIG. 4 and after increasing the dopant concentration offirst layer 36 to layer 36a, a second layer 40 of semiconductivematerial is provided over first layer 36a and to within first remainingopening 38. Second layer 40 as deposited is provided to have an averagelow conductivity enhancing dopant concentration from 0 atoms/cm³ toabout 5×10¹⁸ atoms/cm³. Preferably, layer 40 constitutes the same basesemiconductive material of layer 36, with the preferred material beingsilicon. In this described example, second layer 40 is deposited tocompletely fill first remaining opening 38.

Referring to FIG. 5, the average conductivity enhancing dopantconcentration of second layer 40 is increased to greater than or equalto about 1×10¹⁹ atoms/cm³, and preferably to greater than 5×10²⁰atoms/cm³, to provide a second layer 40a. Again, such diffusion can beconducted by gas diffusion. Alternately if adequate, such diffusion canbe conducted by out diffusion of conductivity enhancing impurity formlayer 36a. In such event, concentration of dopant impurity within layer36a will be provided to be significantly greater than 1×10¹⁹ atoms/cm³to enable an average resultant overall concentration of the pluggingmaterial which will be greater than 1×10¹⁹ atoms/cm³. Subsequently, anouter conductive layer 42 can be provided to provide a desired thicknessof a conductive layer above molding layer 32 for patterning intoconductive lines or other circuit components. The resultant constructiondefines a conductively doped semiconductive material plug 44 withincontact opening 34.

Layers 36 and 40 as-deposited by way of example only can alternately beprovided as amorphous silicon or as polycrystalline silicon. For exampleas known to people skilled in the art, the deposition temperature of585° C. defines a transition temperature which is determinative ofwhether a silicon layer as deposited is amorphous or polycrystalline.Depositions at greater than 585° C. tend to inherently bepolycrystalline, whereas deposition temperatures below 585° C. tend toinherently be amorphous. If deposited as amorphous, subsequent waferprocessing typically subjects the silicon material to effective thermalconditions to transform the amorphous layer into a polycrystallinesilicon material. Regardless, preferably the provision of the first andsecond layers and the increasing of the respective dopant concentrationsoccur in a single chemical vapor deposition reactor without breakingvacuum among the processing steps. Also preferably, layers 36 and 40as-deposited prior to increasing dopant concentrations are preferablyprovided to have minimal or no conductivity dopant concentration tomaximize the conformal deposition effect.

The above described process completely filled contact opening 34 in onlytwo deposition steps. Alternately, a larger number of lightly dopedlayers might be provided for completely filling the contact openings.Typically, the higher the desired conductivity dopant concentration, themore and thinner the deposited layers will desirably be in order tofacilitate conformality and achieve resultant high dopant concentration.Preferably, each intervening layer will be subjected to a gas diffusiondoping immediately after its deposition, although such might beeliminated with respect to some intervening layers with adequate dopingthereof being provided by out diffusion from previous or subsequentlydeposited layers. Regardless, the resultant effect will be tosubstantially fill contact opening 34 with semiconductive materialhaving an average conductivity enhancing dopant concentration of greaterthan or equal to about 1×10¹⁹ atoms/cm³.

FIG. 6 illustrates such an alternate embodiment wafer fragment 50. Likenumerals from the first described embodiment are utilized whereappropriate with differences being indicated with the suffix "x" or withdifferent numerals. Here, a series of a first layer 36x, a second layer40x, and a third layer 60 are provided. Layer 36x is provided to athinner thickness to provide a slightly wider first remaining opening38x. Layer 40x is deposited to a thickness which less than completelyfills first remaining contact opening 38x, thus leaving a secondremaining opening 70. Third layer 60 of semiconductive material isprovided over second layer 40x and to within second remaining opening70, and initially provided to an average conductivity enhancing dopantconcentration of from 0 atoms/cm³ to about 5×10¹⁸ atoms/cm³.Subsequently, its concentration is increased to greater than or equal toabout 1×10¹⁹ atoms/cm³.

Below are two examples.

Run # 1:

Pressure: 80 Torr

Temperature: 630 degrees C.

SiH₄ flow: 0.5 slm

Deposit for 150 seconds to get 3000 Angstroms thick undoped layer, thenturn off SiH₄, and turn on PH₃. Run PH₃ for 60 seconds. Turn off PH₃,and turn on SiH₄ at 0.5 slm for 150 seconds at 630 degrees C. to getanother 3000 Angstroms thick undoped layer. Activation anneal at 1000degrees C. for 20 seconds provided a doped film of overall averagedopant concentration of greater than 1×10¹⁹ atoms/cm³. Bulk resistivitywas 1500 microohm-cm.

Run # 2:

Same as above, except PH₃ treatment was at 800 degrees C. Bulkresistivity was 1000 microohm-cm.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A semiconductor processing method of forming a conductivelydoped polysilicon plug within a contact opening comprising the followingsteps:forming a node location to which electrical connection with aconductively doped polysilicon plug is to be made; forming a plugmolding layer outwardly of the node location; forming a contact openingthrough the plug molding layer to the node location, the contact openinghaving an opening width; forming a first layer of amorphous silicon overthe molding layer to within the contact opening, the first layer beingformed to a thickness which is less than one-half the contact openingwidth to less than completely fill the contact opening with the firstlayer and leave a first remaining opening, the first layer of amorphoussilicon being substantially undoped in having an average conductivityenhancing dopant concentration from 0 atoms/cm³ to about 5×10¹⁸atoms/cm³ ; after forming the first layer within the contact opening,increasing the average conductivity enhancing dopant concentration ofthe first layer by a gas diffusion process to greater than or equal toabout 1×10¹⁹ atoms/cm³, the gas diffusion process providing dopantsubstantially uniformly throughout an entirety of the first layer withinthe contact opening; after increasing the dopant concentration of thefirst layer, forming a second layer of amorphous silicon over the firstlayer and to within the first remaining opening, the second layer ofamorphous silicon being substantially undoped after forming the secondlayer within the first remaining opening, increasing the averageconductivity enhancing dopant concentration of the second layer by a gasdiffusion process to greater than or equal to about 1×10¹⁹ atoms/cm³,the gas diffusion process providing dopant substantially uniformlythroughout an entirety of the second layer within the first remainingopening; transforming the first layer to polysilicon; transforming thesecond layer to polysilicon; and the first and second transformed layersdefining at least a portion of a conductively doped semiconductivematerial plug within the contact opening.
 2. The method of claim 1wherein the second layer only partially fills the first remainingopening to leave a second remaining opening, the method furthercomprising:forming a third layer of amorphous silicon over the secondlayer and to within the second remaining opening; providing a dopantwithin the third layer of amorphous silicon; and transforming the thirdlayer to polysilicon.